Many boats are powered by an engine supported outboard and hydraulically controlled from a steering wheel located remotely from the engine. A hydraulic steering assembly is attached to the tiller arm of the engine and moved in response to hydraulic pressure created during rotation of the steering wheel.
The prior art hydraulic steering assemblies teach the advantages of continuously supporting a hydraulic piston rod parallel to the tilt tube axis of the engine and then attaching a travelling cylinder to the tiller arm. As shown in the U.S. Pat. No. 4,373,920 to Hall et al, issued Feb. 15, 1983, the travelling cylinder can be attached to the tiller arm by a slider mechanism wherein a lost motion connection is established between the tiller arm and the cylinder in order to compensate for the arcuate movement of the tiller arm. Alternatively, a drag link mechanism can be pivotally attached between one end of the cylinder and the tiller arm. The slider type and drag link type connections each have unique advantages and disadvantages.
The advantages of the drag link is that it is strong and simple. The primary disadvantage is that the drag link must be very long in order to maximize force transfer between the cylinder and the tiller arm. That is, if the drag link is very short, at certain angular positions of the tiller arm it will cock relative to the movement of the cylinder and apply reactionary forces to the cylinder nearly transverse to the direction of cylinder travel. In order to prevent this, a long drag link is typically attached to one end of the cylinder. However, the end of the cylinder adjacent the drag link attachment experiences higher loads than the other end of the cylinder. These loads have a component force in directions transverse to the piston rod causing the hydraulic seals between the cylinder and the piston rod to wear rapidly and hence, leak hydraulic fluid.
Alternatively, the slider type connection between the cylinder and the tiller arm is advantageous in that the connection can be made at the mid point between the ends of the cylinder, thereby evenly distributing the loads between the ends of cylinder, and hence preserving the life of the hydraulic seals. Also, the slider connection is advantageous in that the loads typically do not have components of force in directions transverse to the piston rod. However, the slider type connection has the inherent disadvantage that the sliding surfaces frequently bind due to wear. Also, lost motion connections are susceptible to seizure when debris becomes wedged between the sliding surfaces.